1-Getting ready to bake Coffee Cake Cookies: First, preheat your oven to 375°F (190°C) and line two baking sheets with parchment paper to keep things neat and prevent sticking. This quick prep sets the stage for cookies that turn out soft and full of flavor.

2-Next: beat the butter and sugars together on medium-high speed for 3 to 4 minutes until they become light and fluffy this creates that perfect base for the dough. Then, add the egg, egg yolk, and vanilla; mix on low speed until smooth, blending everything nicely. Gradually stir in the baking powder, baking soda, salt, cornstarch, cinnamon, and flour, mixing gently until just combined to avoid overworking the dough.

3-Scoop the dough: into 3-tablespoon balls and place six per sheet, pressing an indentation into each one. For the crumb topping, combine its ingredients and mix until crumbly, then fill each indentation with a handful. Bake for 9 to 12 minutes until the edges turn golden brown, and shape them into circles right after baking for a polished look. Once cooled, mix the glaze with powdered sugar, cinnamon, and milk, then drizzle it over the cookies for a sweet finish.